It is proposed to determine the mechanism in which vitamin K is required for the gamma-carboxylation of specific glutamyl residues of the preformed vitamin K-dependent proteins. The soluble enzyme system has been developed using detergent solubilized nutritionally vitamin K-deficient rat liver microsomes, which will carry out the carboxylation. The absolute additive requirements for this system are CO2, vitamin K hydroquinone and molecular oxygen. The system is stimulated by dithiothreitol. This year's work will be devoted to the purification and isolation of the enzyme system which carries out the carboxylation and the role of each of the added components required.